In 1350 a prince of U-Thong founded the city of Ayutthaya. The new Kingdom rapidly developed into the most powerful and the wealthiest state in South-East Asia. About 1430 its army, after repeated raids into the Khmer Kingdom, destroyed the city of Angkor. A few years later Sukhothai, which had long been subject to it, was incorporated into the state of Ayutthaya. Until the 13th century U-Thong, like Lopburi, had been a centre of Khmer culture, and its art bears the stamp of the Khmer tradition. After the conquest of Sukhothai the influence of the Sukhothai style predominated, until a new style characteristic of Ayutthaya developed The rulers of Ayutthaya considered themselves heirs of both, the Thai tradition of Sukhothai and the Khmer tradition of Angkor. Though they were Theravada Buddhists they adopted the Hindu ceremonial of the Cambodian court. The cities were adorned with magnificent buildings and the arts flourished at the splendour loving court. But in 1767, after protracted struggles, the Burmese attacked Ayutthaya, plundered its treasures and burned the city, which was totally destroyed.

A characteristic feature of the architecture of the Ayutthaya period is the Thai prang. Its model was the temple tower of the Khmers, representing the sacred Mount Meru. In recent years secret chambers have been found in the substructures of several of these prangs, which were adorned with frescoes. The influence of Khmer architecture is obvious in Wat Chai Wattanaram, built by King Prasad Thong (1630 – 1655). The tradition of Sukhothai was continued in the bell-shaped chedis, one of the favourite types had a square ground-plan. The principal buildings of the temples show the ancient style. In the wiharn the slit windows are gradually replaced by rectangular ones, often with decorative gables. There was a further development and exaggeration of the tiered “telescope roofs”.

Of the famous palaces of Ayutthaya none survived the great fire that destroyed the city. They were built of wood, and thus quickly perished. In Lopburi a wiharn, of Wat Sao Thong preserves the appearance of the Ayutthaya period. This building, called `Khurasan”, was originally erected for the Persian ambassadors at the court of King Narai. We know from reports of European travellers that the temples and palaces must have closely resembled the wats in present day Bangkok.

The sculpture of U-Thong was based on the Khmer style, but without slavish imitation. The figures produce a powerful and solemn effect: there is a sharp contrast between the erect body and the horizontal position of the legs in the seated figures. The faces are almost cubical, the hair being indicated by very small curls. The line of hair on the face is clearly marked. In early specimens the protuberance on the head ends in a conical form, in later ones in a sphere or a lotus-bud. At about the middle of the 15th century the U-Thong style, under the influence of Sukhothai, begins to change into the Ayutthaya or “national” style. The fully-developed Ayutthaya style is best seen in the standing figures. The face is longish, crowned by a broad diadem, and on top of the head a cone of flat rings bears the traditional lotus bud. The ear lobes are adorned with earrings, and the clothing falls from the shoulders so as to stand away from the legs, giving the figures a bell shaped outline.

The magnificence of the Ayutthaya court found expression in a new type of Buddha figure, the “Buddha in princely attire”. Late specimens of this type degenerate into formless masses covered with ornaments. In the final years of its 300 years’ history the Ayutthaya style is completely decadent. At the end of the 17th century the Thai passion for decoration reached its peak. Lacquer work, niello silver, plaster ornamentation, wood carving and ceramics are all of extraordinary splendour.